Method of making an electrical heating element

ABSTRACT

METHOD OF MAKING AN ELECTRICAL HEATING ELEMENT WHICH INCLUDES CUTTING A PLANAR RESISTANCE MEMBER INTO A PLURALITY OF LATERALLY INTERCONNECTED STRIPS AND BONDING INSULATING MATERIAL ABOUT THE STRIPS. THE INSULATING MATERIAL IS PREFERABLY A THERMOPLASTIC MATERIAL AND IS PREFERABLY AFFIXED BY DIPPING THE STRIP INTO LIQUIFIED MATERIAL. THE INSULATING MATERIAL HAS A THICKNESS OF FROM .0025.006 INCH WITH PREFERRED THICKNESS BEING .001 INCH. AN ELECTRICAL HEATING ELEMENT IS ALSO DESCRIBED WHICH COMPRISES A RESISTANCE MEMBER HAVING INSULATING BONDED THERETO. THE RESISTANCE MEMBER IS FORMED OF AN INTEGRAL INTERCONNECTED PLURALITY OF LATERALLY DISPOSED MEMBERS WITH EACH MEMBER CONNECTED TO THE ADJACENT MEMBER AT AN OPPOSITE SIDE PORTION. A WATER HEATER IS SHOWN WHICH INCLUDES A WATER-CONTAINING TANK HAVING INLET AND OUTLET CONDUITS. AN ELECTRICALLY OPERATED HEATER MEMBER IS DISPOSED WITHIN THE TANK AND A PRESSURE-CONTROLLED SWITCH IS PROVIDED TO RENDER THE HEATER MEMBER INOPERATIVE WHEN THE WATER WITHIN THE TANK FALLS BELOW A PREDETERMINED LEVEL.

Nov. 23, 1971 J. w. WELSH 3,621,566

METHOD OF MAKING AN ELECTRICAL HEATING ELEMENT Filed May '7, 1969 2Sheets-Sheet 1 FIG.|

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JAMES W. WE L SH BY J my /3 (A ATTORNEY NOV. 23, 1971 w WELSH I3,621,566

METHOD OF MAKING AN ELECTRICAL HEATING ELEMENT Filed May 7, 1969 2Shoots-Shoot 2 g INVHNTOR.

JAMES w. WELSH BY ATTORNEY United States Patent 3,621,566 METHOD OFMAKING AN ELECTRICAL HEATING ELEMENT James W. Welsh, Summit, 'N.J.,assignor to Standard Motor Products, Inc., Long Island City, N.Y.

Filed May 7, 1969, Ser. No. 822,575 Int. Cl. H01c 17/00 US. Cl. 29-610 6Claims ABSTRACT OF THE DISCLOSURE Method of making an electrical heatingelement which 'includes cutting a planar resistance member into aplurality of laterally interconnected strips and bonding insulatingmaterial about the strips. The insulating material is preferably athermoplastic material and is preferably affixed by dipping the stripinto liquified material. The insulating material has a thickness of from.0025- .006 inch with preferred thickness being .001 inch.

An electrical heating element is also described which comprises aresistance member having insulation bonded thereto. The resistancemember is formed of an integral interconnected plurality of laterallydisposed members with each member connected to the adjacent member at anopposite side portion.

A water heater is shown which includes a water-containing tank havinginlet and outlet conduits. An electrically operated heater member isdisposed within the tank and a pressure-controlled switch is provided torender the heater member inoperative when the water within the tankfalls below a predetermined level.

DESCRIPTION OF THE INVENTION This invention relates to a method ofmaking an electrical heating element, to the electrical heating elementitself, and to a water heater which includes the electrical heatingelement of this invention.

conventionally, electrical heating elements which are utilized invarious types of heating devices are made of a resistance member,preferably a resistance wire, which resistance member is surrounded byinsulation and generally encased in a metallic housing. Conventionalresistance members are rather costly to manufacture and, by reason ofdeposits which form on the outside housing tend to burn out under evenmoderate load. Also, where such conventional resistance members are usedin water heaters, a galvanic action occurred between the outside housingand the heater jacket which caused premature failure.

I have discovered a novel method of making such electrical heatingelement which avoids the disadvantages of the prior devices.

In the first place, the electrical heating element is made of a singleplanar resistance member. This resistance member can be of relativelylow cost material such as, for example, nickel-chrome alloy, iron orsteel. The resistance member is then cut into a plurality ofinterconnected strips. This step can be performed extremely rapidly bymeans of the conventional cutting die. Thereafter, insulating materialis bonded to the cut resistance member. This step is also rapid sincethe preferable method of performing the operation is to merely dip thecut resistance member into liquified thermoplastic insulating material,and then squeeze the resistance member between heated plates.

The interconnected insulating strips can then be utilized in variousways as heating elements. The strips can be partially separated andsecured to a stem member and lead-in wires then attached. Alternatively,the strip Patented Nov. 23, 1971 Ice material formed can be elongatedand wrapped about a form. Removal of the form will produce a relativelystrong and stable heating element.

The heating element made by the method of this invention can be disposedinto a heating device such as, a water heater. When the heating elementstructure of this invention is utilized in a water heater, theinsulation on the heating element is of a non-stick type. Therefore,deposits normally do not build up on this structure. However, aself-cleaning action is also produced since the heated wire is free toexpand within the insulation, which is flexible. In the water heatershown in this invention, additional novel structure is provided whichincludes a pressure control switch member which can be utilized torender the heater inoperative when the water in the device falls below apredetermined level. The leadin plug of the heating element of thisinvention, when utilized in connection with a water heater, can bemolded because the heating element does not produce the large quantitiesof unusable heat which are normally produced by conventional methods.

The above constitutes a brief description of this invention and some ofthe objects and advantages thereof. Other objects and advantages of thisinvention will become apparent to the reader of this specification asthe description proceeds.

The invention will be further described by reference to the accompanyingdrawing which is made a part of this specification.

FIG. 1 is a longitudinal cross-sectional view of a water heater made inaccordance with this invention.

FIG. 2 is a detailed side elevational view on a large scale of one formof the electrical heating element made in accordance with thisinvention.

FIG. 3(a) is a plan view of the resistance member prior to its formationinto an electrical heating element.

FIG. 3(b) is a view similar to that of FIG. 3(a) but showing the formassumed by the resistance member after being cut into a plurality ofinterconnected strips.

FIG. 3(a) is a view similar to that of FIG. 3(b) but showing the mannerof afiixing the steel member to the device after the resistance memberhas been insulated.

FIG. 4 is a fragmentary side elevational view of the heating elementformed by the method described in this invention.

FIG. 4(a) is an end view of the electrical heating element shown in FIG.4.

FIG. 5 is a fragmentary front elevational view showing the manner inwhich a resistance member can be formed by an alternative methoddescribed in this invention. In this figure the removable forming memberis shown in fragmentary form about the formed resistance member.

FIG. 6 is a cross-sectional view taken along line .66 of FIG. 5.

FIG. 7 is a front elevational view of the electrical heating elementformed utilizing the method described.

FIG. 7(a) is an end view of the form of electrical heating element shownin FIG. 7.

FIG. 8 is a detailed view of one form of lead-in element that can beused in connection with the electrical heating device of this invention.

The invention will now be further described by reference to the specificforms thereof as shown in the accompanying drawings. However, the readeris cautioned to note that the specific forms of this invention asillustrated herein are merely for illustrative purposes and purposes ofexample only. Various changes and modifications may, obviously, be madewithin the spirit and scope of this invention.

The method of manufacture of the electrical heating element of thisinvention is illustrated in FIGS. 3(a), 3(b), 3(0), 4, 4(a), 5, 6, 7 and7(a). The first step of constructing such an electrical heating elementis the obtaining of a resistance member 11 shown in FIG. 3(a). Thisresistance member may be iron, steel, nickel-iron, nickel-chromium, orany other conducting material. The material should be relatively thickand preferably from about .001 to .010 inch. The thickness of thematerial is, of course, not material and any suitable thickness can beused. However, of course, the resistance of the element will depend uponthe thickness of the material and the material used.

The resistance member 11 is then cut into a plurality of interconnectedlaterally disposed strips 12 by means of a forming die into theconfiguration shown in FIG. 3(b). Insulating material is then bonded tothe cut resistance member preferably by dipping the resistance memberinto a liquified thermoplasticsuch as Teflon made by E. I. du Font andCo., nylon or Kel-F made by Minnesota Mining and Manufacturing Company.The resistance member is then removed from the thermoplastic insulatingmaterial and allowed to cool. Normally, the insulating material mustthen be baked to produce a proper bond to the resistance member.However, such baking normally produces shrinkage and capillary actionwhich tends to expose the end portions of the resistance member.Therefore, after the baking step, it is preferable to place theinsulated resistance member between a pair of heated plates which causesthe insulating material to flow gutwardly around the outer portions ofthe resistance member. Thereafter, a stem member 13 may be secured tothe resistance member as shown in FIG. 3(c) and FIG. 4 by sliding thestern member through the resistance member and then securing the sternmember to the resistance member by rivets 14. It is to be noted that inthe form of invention shown in FIG. 4 the stem member is secured to theresistance member at only a single point so that the resistance membermay move downwardly and thus become a part of an automatic shutofidevice as will be subsequently explained.

Alternatively, the insulated resistance element may be separated and thestrip so produced wound about a form 15 thereby producing theconfiguration shown in FIG. 5. This may then be optionally secured to astem member 13 as shown in FIG. 7.

The heating element of this invention can be utilized in variouselectrical heating devices. FIGS. 1, 2 and 8 show the method ofutilizing the heating element of this invention in a Water heater. Thewater heater consists of a tank 15 which preferably is insulated by aninsulating jacket (not shown). Operatively connected to the tank is awater inward conduit 17 and a water outlet 18. A thermostat 19 isdisposed between wires 20 and 21 and a switch 22 is disposed betweenwires 20 and 23. Wire 24 is also provided. Wires 23 and 24 are connectedto a source of electrical power. Wires 25 and 26 are embedded in aconnector 27 which bears a threaded portion 28 on the outside thereof.Wire 26 is in turn connected to stem 13 (FIG. 2).

Wire 25 is normally disconnected from plunger 27. Plunger 27 is normallymaintained in the disconnected position by coil spring 28 which isdisposed about plunger 27 and which is disposed within recess 29.Plunger 27 is movable within recess 29 and water is kept out of thisrecess by seal 30. Plunger 27 bears a pressure portion 31 thereupon andis in turn connected to resistance member 11. Wire 25 is connected towire 24 and wire 26 connected to wire 21.

With the foregoing specific description the operation of this inventioncan now be explained.

In the normal condition, where no water is present within tank 16,plunger 27 is in the up (disconnected) position. At this point no powerflows into resistance member 11.

When water 35 rises within tank 16 above a predetermined level itapplies pressure to seat 31 which in turn moves plunger 27 in a downwardposition thereby causing plunger 27 to make electrical contact with wire25. If switch 22 is now closed and thermostat 19 at a temperature belowthe temperature that the water is to assume, power will now flow intoresistance element 11 and cause water 35 to be heated. Power can bemanually disconnected at any time by opening switch 22 or power will bedisconnected if the temperature of the water reaches the predeterminedtemperature and thermostat 19 opens. Power will also be disconnected ifwater 35 falls below a predetermined level and pressure is no longerapplied to seat 35.

The foregoing sets forth the manner in which the objects of thisinvention are achieved.

I claim:

1. A method of making an electrical heating element comprising the stepsof obtaining a planar metallic member of relatively high resistancehaving a thickness of from .001 to .010 inch, cutting said member into aplurality of laterally interconnected parallel strips having alternatelycut-out lateral portions, dipping said formed member into a heatedliquified thermoplastic insulating material, removing said formed memberfrom said liquified insulating material and allowing it to cool, bakingsaid formed member until the insulating material bonds firmly to theresistance member, and thence placing said resulting product between apair of heated plates until the insulating material flows outwardlyaround the outer portions of the resistance member.

2. A method as described in claim 1 including the additional step ofplacing a stem member within said completed formed member with saidstern member passing alternately above and below adjacent interconnectedparallel strips.

3. A method as described in claim 2, said stern member beingsubstantially centrally disposed with respect to said strips.

4. A method as described in claim 3, said stem member being secured tosaid resistance member.

5. A method as described in claim 4, said stem member being secured tosaid resistance member at a single point onl g A method as described inclaim 5, the said single point of securement of said stern member tosaid strip being at the upper end thereof.

References Cited UNITED STATES PATENTS 953,393 3/1910 Parkhurst 29610 X2,357,906 9/1944 Osterheld 338-244 2,432,800 12/ 1947 Reichold 296 10 X2,865,795 12/1958 Morrison, Jr 1l7230 3,028,265 4/1962 Wareham 117128.4X 3,340,216 9/l967 Mack 117132 X 3,408,735 11/1968 Eisler 29-6103,516,154 6/1970 Cooper et al. 29611 JOHN F. CAMPBELL, Primary ExaminerV. A. DI PALMA, Assistant Examiner U.S. Cl. X.R.

